Field of the Disclosure
Embodiments of the present application relates to the art of a belt-driven continuously variable transmission using a chain belt.
Discussion of the Related Art
JP-A-2013-7438 describes a continuously variable transmission comprising an input pulley rotated by a power of a prime mover, an output pulley transmitting the power to an output side of a powertrain, and a chain running between those pulleys. In the continuously variable transmission taught by JP-A-2013-7438, a speed ratio may be varied infinitely by changing widths of chain grooves of the pulleys. According to the teachings of JP-A-2013-7438, in order to suppress string vibrations of the chain belt, a guide rail is arranged between the pulleys in a pivotal manner with respect to a pin.
However, if the chain belt breaks in the continuously variable transmission taught by JP-A-2013-7438, the broken chain may collide against a casing of the transmission to generate intense noise. For example the broken chain may be centrifugally cast off the pulley and collide against the casing. In this case, a crash impact of the broken chain is increased if a rotational speed of the pulley is fast. Alternatively, one end of the broken chain may be caught in the pulley and the other end of the broken chain may flap to collide against the casing repeatedly. In this case, the broken chain may be caught easily by the pulley in which a running diameter of the chain groove is smaller.